Missing touch option in Rails has_many relation

Question

I have 2 Rails models: Book and Category, where a book belongs_to a category, a category has_many books.

The category name is shown in each book's page, and pages are cached.

If I change a category name (say, from 'Sci Fi' to 'Science Fiction'), then all corresponding book pages will be stale, and books need to be "touched" in order to trigger HTML regeneration.

It would seem to make sense to be able to do:

class Category << ActiveRecord::Base
  has_many :books, touch: true
end

But the option is unavailable, I guess because the touch mechanism would instantiate each object, which could result in a major performance hit for has_many relationships.

To avoid that, I am using raw SQL as follows:

class Category << ActiveRecord::Base
  has_many :books
  after_update -> {
    ActiveRecord::Base.connection.execute "UPDATE books SET updated_at='#{current_time_string}' WHERE category_id=#{id})"
  }
end

Which is pretty terrible. Is there a better way?

Answer 1

You can't use touch on has_many association, it works only with belongs_to, that's a fact.

If I understand correctly what you want, the answers with touch:true in the Book model won't work, because the Book object will not be updated when You change the Category model and the view will not regenerating.

So I think your solution is the best for that. (You can use also books.update_all(updated_at: Time.now))